Add missing categories to the "all" index and sprinkle difficulty-level
settings to the projects that lacked them. The "all" index is now fully
organized.

[[!template id=project
title="Defragmentation for FFS"
contact="""
[tech-kern](mailto:tech-kern@NetBSD.org)
"""
category="kernel"
difficulty="easy"
description="""
Heavily used file systems tend to spread the blocks all over the disk,
especially if free space is scarce. Traditionally dump/restore have been used to
recreate the file system, but this is not acceptable for current disk
sizes. Since resize_ffs has to relocate blocks during shrinking anyway, it
should be possible to extend it to full reordering and defragmentation.
"""
]]